|Title:||Oxygen transport in the arterial vasculature of the residual limb after trans-femoral amputation|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Leg -- Amputation
|Pages:||xxiii, 181 pages : color illustrations|
|Abstract:||Numerous musculoskeletal injuries are caused by earthquakes, such as lacerations, fractures, and soft-tissue contusions or sprains. And there are 3-20% of influenced people suffering crush injuries, in which injuries of the lower limb (74%) are the most common. Moreover, there were 2.26 million amputees in China by 2006. After Whenchuan and Lushan earthquakes, the number of amputees has considerably increased. It attracts a vast amount of public attention in contemporary society. After the amputees wearing prostheses, there are a number of health problems in the residual limbs which are disruptive to amputees' daily lives. These problems hinder their clinical rehabilitation and may even threaten their physical health. The development of these problems including blisters, edema, pressure ulcers, damage to deep soft tissue and muscle atrophy is related to the biomechanical mechanism, while the fundamental mechanisms of these problems have not been fully elucidated. Thus, studies on residuum disorders are of great significance in biomechanical research. The spatial vasculature of the residual limb is changed significantly by lower-limb amputation. Changes in the vasculature affect the hemodynamic status and oxygen transport in the circulatory system. And understanding the hemodynamic status and oxygen transport in the residuum is beneficial in evaluating the residuum status. Few investigations have focused on the blood flow and oxygen transport systematically in the circulatory system of the residual limb due to the complex vasculature. In order to understand the blood flow and oxygen transport systematically in the arterial system of the residual limb after amputation, computational and experimental investigations about oxygen distribution and hemodynamic responses were implemented in this study and included four parts as follows. First, computational fluid dynamics models of the descending branches of the lateral femoral circumflex artery (DLFCA) coupled with oxygen transport in both the residuum and the sound limb were established, and three inflow velocities were applied at inlet to figure out the effect of exercise on oxygen transport in residuum DLFCA. Consequently, the investigation of oxygen transport in the residuum vasculature was suggested to be valuable in understanding the health status of the residuum after amputation, and the joint consideration of WSS and oxygen distribution was required in determining the rate of the atherosclerosis development in residuum arteries. Additionally, exercise was indicated to be favourable for enhancing oxygen content in DLFCA of the residual limb and reducing the possibility of the formation of the atherosclerotic plaque in residuum arteries. Second, the oxygen concentration in the arteries could not be noninvasively monitored in clinical research, and a three-dimensional (3D) numerical simulation of the systemic arterial tree is complicated and requires considerable computational resources and time. Thus, transmission line equations of oxygen transport in the arteries were firstly proposed according to the theory of oxygen transport and fluid transmission line equations. And these equations were numerically verified through the comparison between a 3D computational simulation of oxygen transport in the vascular model and a lumped parameter model of oxygen transport. These transmission line equations are treated as the theoretical basis for the establishment of the lumped parameter model of oxygen transport, and this model can be applied for numerically predicting the oxygen distribution in the systemic arterial tree with fewer computational resources and less time. Moreover, these transmission line equations of oxygen transport can also be regarded as the theoretical basis for developing transmission line equations of other substances in blood.|
Third, transmission line equations of mass transport in arteries have been proposed, and these equations offer a more efficient scheme for investigating the systemic distribution of the substance in the arterial tree. Whereas, the derivation of these equations in arterioles and capillaries is lacked. Transmission line equations of mass transport in arterioles and capillaries were developed, and these equations were derived based on the transmission line equations of mass transport in arteries and mass transport theory in microvessels. These equations were verified through the comparison of the numerical prediction based on the developed equations with the previous in vitro experimental studies. The transmission line equations of mass transport in arterioles and capillaries are not only applied in constructing the lumped parameter model of mass transport for predicting the systemic distribution of the substance concentration in the microvascular tree, but also regarded as the supplement to the theoretical basis for establishing the lumped parameter model of the entire vascular system including arteries, arterioles, and capillaries. Forth, oxygen distribution in the residual limb changes due to the vasculature transformation after trans-femoral amputation, and changes in oxygen content play a significant role in the developments of health problems of the trans-femoral residuum. Oxygen content in the residual limb mainly depends on oxygen transport in the residuum vasculature. Few studies focused on oxygen transport in the arteries of the residual limb. We developed a coupling computational model of blood flow and oxygen transport in the residuum arteries to predict oxygen distribution, and the Windkessel model and the lumped parameter model of oxygen transport were applied as the boundary conditions at outlets of the vascular model. The boundary condition with the lumped parameter model of oxygen transport was verified through the comparisons between the non-elongated vascular models with the lumped parameter models and the elongated models. Moreover, an in vitro experiment with a three-dimensional (3D) printing replica of the residuum vasculature was carried out to validate the computational simulation. The proposed boundary condition with the lumped parameter model was determined to be reliable for simulating the effect of downstream vessels on oxygen transport in the vascular model. According to the numerical results of the 3D computational model with the developed boundary conditionof oxygen transport, the effect of inflow velocity on oxygen distribution was indicated to be much smaller than that of backflow during a pulsation cycle. Moreover, with the joint consideration of Sh, WSS, and oxygen content in tissues, the adjustment of inflow and backflow during a cycle was proposed to alleviate the risk of the residuum disorder.
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